One type of earth boring bit has a steel body with at least one bit leg, normally three, or it could have four, such as for a pilot reamer. A cone with cutting elements is rotatably mounted to a bearing pin depending from each bit leg. Hardfacing is typically applied to part of the outer surface of each bit leg. Alternately, the bit leg may have tungsten carbide compacts pressed into the outer surface alone or in combination with hardfacing. The hardfacing is usually a mixture of carbide particles in a matrix of iron, nickel or cobalt, or alloys thereof.
In some geographic areas, bit legs have been known to break. The fracture is often in the vicinity of the weld on the ball plug. The ball plug and weld close the outer end of a passage for inserting balls into a locking arrangement between the cone and the bearing pin.